1. Field of the Invention
The invention relates to a temperature sensing device. More particularly, the invention relates to a temperature sensing device that can control the conducting number of current sources for generating a temperature voltage.
2. Description of the Related Art
A temperature sensor is an electronic device that can convert the temperature into digital information. The existing temperature sensors are developed to have the improved measurement accuracy and the reduced volume and thus have been extensively applied to various electronic equipments.
Among a variety of temperature sensors, a semiconductor-type temperature sensor obtains the ambient temperature by comparing a temperature voltage having a positive temperature coefficient with a reference voltage that is not changed together with the temperature. Here, the positive temperature coefficient is in direct proportion to the absolute temperature. The voltage having the positive temperature coefficient can be generated by a proportional-to-absolute-temperature (PTAT) circuit, and a bandgap reference circuit allows the output reference voltage not to be changed together with the temperature.
Hence, the PTAT circuit of the temperature sensor can generate the current IPTAT with the positive temperature coefficient, direct the current IPTAT to serially-connected resistors, and obtain the temperature voltage having the positive temperature coefficient from the endpoints of the serially-connected resistors. A multiplexer and a comparator of the temperature sensor are then applied to respectively obtain the corresponding temperature voltage and compare the potential of the temperature voltage with the potential of the reference voltage, so as to determine the ambient temperature.
In order to have accurate resistances, the serially-connected resistors need a relative large chip area to obtain the accurate temperature voltage generated during the current IPTAT flows through the serially-connected resistors. In case of the semiconductor process drift, the serially-connected resistors are also affected to a great extent. Besides, the more the resistors applied in the temperature sensor, the more the noise caused by the resistors. In order to design the serially-connected resistors, a pull-up resistor electrically connected to the ground voltage may need to have a resistance greater than the resistances of other serially-connected resistors, so as to significantly raise the potential of the temperature voltage for comparing the potential of the temperature voltage with the potential of the reference voltage. This accordingly expands the circuit area of the temperature sensor.
As a result, how to simultaneously improve the temperature measurement accuracy and reduce the circuit volume of the temperature sensor is an issue to be resolved in the research and development of the semiconductor-type temperature sensor.